1. Field of the Invention
This specification relates to a bush bearing used as a journal bearing and a hermetic compressor having the same.
2. Background of the Invention
In general, a hermetic compressor includes a motor for generating a driving force in an inner space of a hermetic case, and a compression part coupled to the motor for compressing a refrigerant. The hermetic compressors may be divided into a reciprocal type, a scroll type, a rotary type, a vibration type and the like according to a refrigerant compression mechanism. The reciprocal type, the scroll type and the rotary type use a rotational force of the motor, while the vibration type uses a reciprocal motion of the motor part.
Among those hermetic compressors, the motor of the hermetic compressor using the rotational force has a crank shaft to transfer the rotational force of the motor to the compression part. For example, the motor of the rotary type hermetic compressor (hereinafter, referred to as a rotary compressor) includes a stator fixed to the hermetic case, a rotor inserted in the stator with a predetermined gap therebetween to be rotatable by interaction with the stator, and a crank shaft coupled to the rotor to transfer the rotational force of the rotor to the compression part.
The compression part includes a cylinder, a rolling piston and a vane for compressing a refrigerant in the cylinder, and a plurality of bearing members for defining a compression space together with the cylinder and supporting the crank shaft. The bearing members are typically located at one side of the motor to support the crank shaft. However, as compressors becomes highly efficient in recent time, a technology of minimizing compressor vibration by installing bearings at both upper and lower ends of the crank shaft has been introduced.
When the bearings are installed at the upper and lower ends of the crank shaft, the upper bearing may generally be implemented as a ball bearing or a bush bearing. Especially, the bush bearing may be made of bimetal, resin (polytetrafluoroethylene (PTFE), typically Teflon), carbon, a solid material and the like. Among others, bimetal, resin and carbon are generally used for a compressor, and the resin-based bush bearing is used the most widely. A bush bearing made of bimetal or carbon is highly resistant to abrasion, and a bush bearing made of resin is excellent in view of a frictional loss due to a low frictional coefficient of the resin.
However, in the configuration of the related art Teflon-based bush bearing, since the Teflon having lubricity is pressed-fitted between porous bronze sintered layers, the Teflon layer is actually formed with a thickness of approximately 20 μm, which is merely as thin as about 20% of the overall thickness of the bush bearing. Consequently, if a friction is generated between an outer circumferential surface of the crank shaft and an inner circumferential surface of the bush bearing, the Teflon layer of the bush bearing may be fast worn away and thereby the metallic bronze sintered layer may come in contact with the crank shaft, resulting in a drastic abrasion of the bush bearing or the crank shaft.